Muchnick was killed in a training exercise in Nevada on Monday.
Flags will remain at half-staff until a burial or memorial.
“Lance Cpl. Muchnick was an American hero whose life was cut short, and we join his family and friends in mourning this tragedy,” Malloy said in a statement. “Our prayers are with all of our armed forces who are serving this nation so bravely.”
Muchnick and six other Marines were killed Monday night at Hawthorne Army Depot in Nevada after a mortar round exploded during a training exercise, according to the Associated Press. Eight others were reported injured, and of those, one died in the hospital.
U.S. Rep. Jim Himes, a Democrat who represents Westport in the 4th Congressional District, said he is heartbroken over Muchnick's death.
"Roger was one of eight bright young men whose lives were cut tragically short this week, and we must never forget his courage and sacrifice," Himes said in a statement Thursday.
"Our men and women in uniform give so much in the defense of this nation, and I know that the community of Westport will be reeling from this loss for a long time to come," Himes continued. "I want to express my deepest sympathies to Roger’s family, friends, and all those whose lives were touched by his.”
Muchnick, who played football and lacrosse at Staples, was fondly recalled by those who knew him.
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